The default Scrypt parameters were designed to do that. The parameters changed in LTC (and copied over in all clones) were weakened to reduce the memory hardness by 99%.
Memory, in general, is cheap.
Fast memory is not. If the memory parameters are large with scrypt, an ASIC could be built using cheap memory with a smaller amount of processing units (or slower/cheaper ones). The LTC scrypt design
seems to be in a very reasonable range where lots of chips can be used, but each requires a reasonably-sized amount of expensive memory and fast buses to keep up. It's difficult to say how it will/would have played out when/if ASICs are designed for the LTC scrypt algorithm. But for now, GPUs being in the sweet spot could only be a good thing imo, botnet coins are no fun.
Well given that sASIC exist with 10x to 20x as much memory (as in on die negligible latency SRAM) as required for "LTC Scrypt" I don't see the "128KB barrier" being much more than paper thin. I mean we are talking about KB here not MB or GB and Moore's law is still alive and well. The only real barrier is that the market cap (and thus annual mining revenue). It is still laughably low. Just like nobody was looking into Bitcoin ASICs when the price was $1 USD per BTC nobody is going to look into LTC ASICs until it is justified. That means either LTC forever remains uselessly small or it sheds it's "ASIC resistance" like a paper dragon when it breaks into any meaningful exchange rate. If LTC sustains a price action above $10 expect to see existing ASIC manufacturers turn their attention there. Remember eventually the margins on BTC Asic production will dry up due to over supply and limited demand. So you have a handful of experienced (by then) companies looking for a market to explooit. Bitcoin hardware is now a commodity play and if LTC prices support it, there is a chance to play out the ASIC mania all over again. Never discount an economic incentive. The idea of making 80%, 90%, 95% or more gross margins on the first batch will be attractive to companies facing paper thin margins, low barriers to entry, and heavy competition. LTC (et all) could have been memory hard but they chose (either by negligence or malice) to set the "barrier" incredibly low. The minimum recommendation by the AUTHOR (not some random guy but the guy who wrote it) is ~20MB of scratch pad. LTC chose to use ~1% of that.